Reactions that are conducted in solution such as, for example, chemical, biological, biochemical, molecular biological reactions, are mostly carried out within a chamber, well or other container, typically made of glass or plastic, and including, for example, test tubes, microcentrifuge tubes, and capillary tubes. There is an ever growing need to increase the throughput of such reactions, particularly with diagnostic assays and screening tests, and to make them faster, cheaper and simpler to perform while at least maintaining, if not increasing, precision and reliability of conventional laboratory processes.
In order to achieve the above mentioned goal, substantial effort has been devoted to miniaturization, parallelization, and integration of various process steps, e.g. by developing microtiter or multi-well plates and microfuidic chips. For example, multi-well plates with 1536 wells and standard footprint have been developed. Conventionally, however, when volumes decrease, other problems increase, such as imprecise liquid metering, liquid evaporation, inefficient mixing, adverse capillary effects due to an increased surface to volume ratio, difficult handling, positioning, optical detection. Moreover, many of the reactions mentioned above require thermal treatment and some require rapid temperature changes, e.g. PCR.
However, many reaction chambers materials are poor thermal conductors with large thermal time-constants and large thermal gradients and hence, long time lags are associated with changing the temperature of the reaction chamber and equilibration of a temperature change throughout the sample volume. Such leads to longer reaction times, non-uniform reaction conditions within a single reaction and lack of reproducibility among multiple reactions, both parallel and sequential.
For multi-well plates comprising up to about 384 wells and which still have relatively large reaction volumes, i.e. several microliters, it is possible to fit the outer side walls of the wells at the bottom of the plate into corresponding holes of a thermal block in order to improve thermal contact and minimize thermal gradients. Another problem, such as condensation at the inner side walls, can be prevented e.g. by heating a cover closing the wells from the top.
For multi-well plates with a higher number of wells, and smaller reaction volumes, however, the matching accuracy between the wells and the thermal block need to be extremely high, thus putting a high demand on manufacturing tolerances. Another problem is the tendency of the wells to deform and of the plate to get jammed with the thermal block.
US 2003/0170883 A1 discloses a multi-well plate that is manufactured from a thermally conductive material, which enables the wells to have relatively rigid walls and makes it easier to handle the multi-well plate. The thermally conductive material can be a metal or a mixture of a polymer and one or more thermally conductive additives. However, multi-well plates made of thermally conductive polymers have a series of disadvantages. In general, such multi-well plates are more expensive because either metal or polymer/additives mixtures are more expensive than basic polymers and because thermal conductive materials alone are not sufficient for some applications, meaning that a top layer of isolative material may be needed through which the temperature can drop. Using different materials in layers may introduce new problems due to selective shrinkage and consequent deformation. Moreover, during manufacture, typically by injection molding, there is a tendency of the additives to form aggregations, i.e. local concentration changes, leading to non-uniform thermal conductivity and thus to a reduced and/or unpredictable thermal performance. Also, the additives may increase the viscosity of the polymer such that injection molding is complicated or even impossible in narrow long flow paths.
US 2002/0072096 A1 discloses a microhole apparatus comprising a substrate, the substrate defining a plurality of sample chambers extending through the substrate and comprising hydrophobic and non-hydrophobic regions. The sample chambers can thus hold samples by surface tension in the form of a thin film, which enables rapid thermal equilibration. Multi-well plates comprising selective hydrophilic/hydrophobic regions require however a complex coating process raising the costs of manufacture. Also, the effect of the surface tension is very much dependent on the liquids used and on the presence of additives such as surfactants, ultimately leading to unpredictable or irreproducible performance. Moreover, stability of the coating, especially when exposed to high temperatures or repeated temperature cycles may be an issue. Also, due to the required aspect ratio of the chambers, a high well density is not obtainable.